getcontext

, setcontext

- get and set current user context

Synopsis

#include <ucontext.h>
intgetcontext(ucontext_t *ucp);

intsetcontext(const ucontext_t *ucp);

Description

The getcontext() function initializes the structure pointed to by ucp to the
current user context of the calling process. The ucontext_t type that
ucp points to defines the user context and includes the contents of the
calling process' machine registers, the signal mask, and the current execution stack.

The setcontext() function restores the user context pointed to by ucp.
A successful call to setcontext() does not return; program execution resumes at
the point specified by the ucp argument passed to setcontext(). The ucp
argument should be created either by a prior call to getcontext(), or
by being passed as an argument to a signal handler. If the
ucp argument was created with getcontext(), program execution continues as if the corresponding
call of getcontext() had just returned. If the ucp argument was
created with makecontext(3C), program execution continues with the function passed to makecontext(3C).
When that function returns, the process continues as if after a call to
setcontext() with the ucp argument that was input to makecontext(3C). If the
ucp argument was passed to a signal handler, program execution continues with the
program instruction following the instruction interrupted by the signal. If the
uc_link member of the ucontext_t structure pointed to by the ucp argument
is equal to 0, then this context is the main context, and the
process will exit when this context returns. The effects of passing
a ucp argument obtained from any other source are unspecified.

Return Values

On successful completion, setcontext() does not return and getcontext() returns 0. Otherwise,
-1 is returned.

Errors

No errors are defined.

Usage

Portable applications should not modify or access the uc_mcontext member of ucontext_t.
A portable application cannot assume that context includes any process-wide static
data, possibly including errno. Users manipulating contexts should take care to handle these
explicitly when required.